In the United States approximately 10% of women of child bearing age smoke marijuana. This study employs a prospective single blind design to explore whether marijuana use in pregnancy poses an independent risk to the growth and development of the fetus. After giving informed consent, 1500 pregnant women receiving prenatal care at Boston City Hospital will be evaluated at their initial prenatal visit (T1), during the third trimester (T2), and following delivery (T3). Detailed interviews, medical record audits, anthropometric measures, and urine assays will be used to determine subjects' health, nutritional status, health habits, and psychoactive drug use during each trimester. It is expected that, compared to self-report, urine assay will reveal a higher proportion of users of marijuana and other psychoactive substances. A physician blind to mothers' history will ascertain outcomes of interest including fetal wastage and the newborn's duration of gestation, intrauterine growth, dysmorphic features, perinatal morbidity, and neurological status. A subsample of infants exposed to marijuana and appropriately matched controls will undergo detailed assessment of neurobehavioral function. It is hypothesized that women who smoke marijuana will differ significantly from non-users on a variety of characteristic (eg. age, parity, nutritional status, and health habits including use of cigarettes, alcohol, and other psychoactive substances) that may adversely effect fetal outcome. Therefore multiple regression analyses will be used to determine whether marijuana use has an independent effect on fetal outcome when interrelated, potentially confounding variables are statistically controlled. In addition, the effects of the frequency and timing of marijuana use upon fetal outcome, and whether discontinuation of marijuana use before the third trimester of pregnancy decreases risk of adverse fetal outcome will be determined. Since marijuana use is so prevalent, the results of this study will have important implications for millions of women nationwide.